The relative roles of contemporary and ancient processes in shaping genetic variation of a generalist fish in a catchment dominated by agriculture

Abstract

1. Conversion of land for agriculture has led to the channelisation of headwater streams and reduced water quality. Resident fish populations are expected to be challenged under such conditions and may experience declines that lead to a loss of neutral genetic variation. 2. However, species-specific responses to recent ecological changes in stream condition and/or range expansion following glacial retreat can also influence the pattern of genetic variation found within and among contemporary populations. To evaluate the relative roles of contemporary and ancient scenarios that are hypothesised to affect the genetics of populations in streams, we studied the creek chub (Semotilus atromaculatus), a common species that is tolerant of stream degradation. 3. We screened eight microsatellite loci on 308 individuals originating from ditches and streams surrounded by agricultural and forested land cover within the St. Joseph River catchment in northeastern Indiana and southern Michigan, U.S.A. 4. We found weak population structure associated with land cover and, in contrast to expectation, higher allelic richness in agricultural streams. Using Bayesian coalescent modelling, the strongest pattern found within the data set was evidence of a population decline throughout the catchment that most likely preceded stream channelisation and land conversion. 5. The results illustrate the complexity of using neutral genetic variation of populations to assay stream quality. Tolerant species may have increased gene flow in channelised streams that leads to an increase in genetic variation. Meanwhile, post-glacial landscape change and subsequent colonisation of nascent freshwater streams appears to shape genetic variation regardless of contemporary land use.

Considering Fish as Recipients of Ecosystem Services Provides a Framework to Formally Link Baseline, Development, and Post-operational Monitoring Programs and Improve Aquatic Impact Assessments for Large Scale Developments

“…With some species, semi-quantitative abundance estimates may also be possible (Wood et al 2021 ). The population genetic analysis described for the baseline phase above are not useful for immediate post-development monitoring, as the patterns reflect demographic changes occurring on decadal and longer timescales (Jordan et al 2013 ). Instead, the same genetic data can be used with individual-level analyses as opposed to population-level analysis.…”

The influence of flow on movement of a headwater specialist in an intermittent urban headwater stream

“…Some headwater specialist fish species take advantage of shifts in flow to move upstream and downstream, and the use of high flows may be more pronounced in intermittent reaches than in perennial streams (Albanese et al, 2004), pointing to the possibility that some species may conform movement behaviour to the flow regimes of urban stream systems. One headwater specialist species with a potentially interesting response to flow is the Creek Chub ( Semotilus atromaculatus ), one of the most common fish encountered in headwaters in northeastern North America (Jordan et al, 2013), with a preference for small and low‐volume streams (Dinsmore, 1962). The specific pattern of their migration and colonisation is debated, with some studies suggesting displacement‐based movement from old to new populations and others supporting the possibility of rapid recolonization events followed by long periods of genetic isolation (Jordan et al, 2013; Skalski et al, 2008).…”

“…One headwater specialist species with a potentially interesting response to flow is the Creek Chub ( Semotilus atromaculatus ), one of the most common fish encountered in headwaters in northeastern North America (Jordan et al, 2013), with a preference for small and low‐volume streams (Dinsmore, 1962). The specific pattern of their migration and colonisation is debated, with some studies suggesting displacement‐based movement from old to new populations and others supporting the possibility of rapid recolonization events followed by long periods of genetic isolation (Jordan et al, 2013; Skalski et al, 2008). Consistent with either scenario, Creek Chub are undeniably one of the first fishes to recolonize heavily impacted stream systems and can serve as a sentinel species for identification of environmental stressors (Fitzgerald et al, 1999) and connectivity in small streams.…”